Nowadays, card systems using non-contact IC cards are broadly used. In addition, a non-contact IC card equipped with a display element has been also used, and an IC card system using a cholesteric liquid crystal as the display element has been proposed. In such a non-contact IC card system, a system configured to be able to realize both stability of data communication and reduction of the driving power of the display element is required. Note that an IC card is also referred to as a smart card.
As an invention to improve stability of data communication, for example, Japanese Laid-open Patent Publication No. 2005-173862 proposes an invention in which, in a non-contact IC card, the level of a received signal is detected, and variable control of the Q factor of the resonance circuit is performed, to stabilize data communication.
However, conventional non-contact IC card systems have following problems. The signal transmission from a non-contact IC card to an IC card reader/writer is performed by load modulation. However, in the case of an IC card equipped with a large-sized display element that covers the entire surface of the IC card, load change occurs as the display element is driven, and the load change is mistakenly regarded as load modulation on the IC card reader/writer side, causing a system error.
In addition, with a large-sized display element that covers the entire surface of the IC card, a large amount of display data is transmitted to the IC card, decreasing the communication speed.
Furthermore, large power consumption is required to drive such a large-sized display element as the one described above, which leads to a shortage of the antenna reception power.